Question

Write functions and deficiency symptoms of following elements:

(a) Ca

(b) Mg

(c) Fe

(d) P

(e) S

Answer 1

(a) Calcium (Ca): The amount of calcium in plants is approximately 0.1 - 3.5%.

Source: Calcium obtained to soil by weathering of anorthite or CaAl₂ Si₂ O₂. Its other common compound is calcium carbonate (CaCO₃) which obtained from lime. It present also in the form of calcium phosphate in soil. Plant absorb calcium in the form of Ca⁺⁺ ions.

Specific Role

• It is most important component of cellwall. The middle lamella is made of calcium pectate.
• It is essential for carry the metabolic process of plant body.
• It controls the permeability of cell membrane.
• It is essential for continuous growth of shoot apex and also for cell division.
• It reduces toxicity converting organic acid to harmless compounds.
• It helps in transportation of amino acid and carbohydrate.
• It increases root growth.
• It is found as calcium oxalate crystals in many plants.
• It helps in formation of cell membrane.
• It takes part in photolysis of water and regulating metabolism.

Deficiency Symptoms

• The cell wall does not form during cell division.
• The root and shoot meristem become dead.
• Roots are poorly developed.
• Chlorosis is produced on the margins of young leaves.

(b) Magnesium (Mg): Its amount in dry weight of plant is 0.5 - 0.7%.

Source: It is found in soil mainly as carbonates (MgSO₃) and dolomite (MgCO₃ . CaCO₃). Plants absorb it as magnesium (Mg ⁺⁺) ions.

Specific Role

• It is the main component of chlorophyll molecule.
• It is intimately associated with the phosphorus metabolism and is particularly essential for the enzymes involved in the phosphate transfer reaction.
• It plays an important role in synthesis of ATP from ADP and inorganic phosphate.
• It activates many enzymes such as carboxilase, hexokinase, phosphorylase dehydrogenase etc.
• It binds sub - units of ribosome together. The formation of dimers and polymers of ribosome depends upon the concentration of Mg⁺⁺ ions.

Deficiency Symptoms

• Interveinal chlorosis is produced in leaves.
• The older leaves are affected first and the younger leaves are affected later on.
• Anthocyanin pigment begins to form due to which red or violet colour begin to form in chlorotic regions.
• The necrotic area begins to form on leaves.
• The vegetative and reproductive growth of plant are reduced.

(c) Iron (Fe): Its amount is 10 - 100 ppm (mg/L) in plants.

Source: In soil iron is found as limonite and pyrite form. It is absorbed by plants in both the forms i. e., ferrous and ferric ions. It is found abundently in acidic soil. The pH of soil controls iron.

Specific Role

• It is main component of porphyrine, cytochrome, peroxidase and catalase.
• It is essential for chlorophyll synthesis.
• It is important component of ferridoxin.
• Iron play an important role in respiratory mechanism.
• It is a component of several electron carriers.

Deficiency Symptoms

• Chlorosis is produced in leaves and become yellow in colour.
• The decomposition of plastids begins.
• Protein synthesis in plant is reduced.
• The symptoms appear first in younger leaves.
• Its deficiency seriously impairs aerobic respiration and other related processes.
• Petioles become short.

(d) Phosphorus: Its amount in dry weight of plant is 0.2 - 0.8%. Phosphorus is one of the most important element for the plants. It is a vital structural component of the nucleic acid, nucleoprotein, phytin, phospholipids, sugar phosphate, ATP, NADP⁺ etc

Source: The soil is the main source of phosphorus for plants. Phosphorus is absorbed by the plants from the soil in the form of phosphate ions H₃PO₄^-  and HPO₄^2-.

Specific Role

• It is component of NAD, NADP⁺ and ATP etc.
• It is also component of RNA, DNA and phospholipids.
• It plays an important role in protein synthesis with the help of oxidation, reduction and energy transfer processes. For example, ADP, NADP⁺ and ATP etc., are substance of phosphate act in photosynthesis and respiration.

Deficiency Symptoms

• Root and stem become weak and small.
• There necrotic regions are formed on leaves and fruits.
• Phosphorus deficiency may cause premature leaf fall and purple anthocyanin pigmentation.
• Plant growth is retarted.
• The activity of cambium is decreased.

(e) Sulphur (S): The amount of sulphur in plants is approximately 0.5 - 1%.

Source: Inorganic sulphur is found in soil in the form of minerals such as pyrite, gipsum, ipsonite and cobohite etc. It is soluble in water in the form of sulphate (SO₄). Some bacteria convert sulphur to sulphate. It is absorbed by plant from soil as sulphate ion.

Specific Role

• It takes part in the formation of several amino acids such as cystein, cystine and methionine etc. Besides, it is main component of vitamins such as biotin, thiamine and it is also a major component of coenzyme - A.
• It helps in seed formation.
• In some plants e.g., mustard, onion, garlic etc., it forms glucoside.

Deficiency Symptoms

• There is a deficiency of sulphurous amino acids due to which sulphurous proteins also reduced and the storage of carbohydrates is increased.
• Leaves exhibit chlorosis. This symptom is first seen in young leaves and then in old leaves.
• Due to the storage of carbohydrates, there is increase in the quantity of thick walled tissues, whereby the stem of plant becomes strong.
• The apical growth of the plant is reduced.